1. Technical Field
The present invention relates to an operation mode changing-over method wherein each of a plurality of nodes connected to a common multiplex transmission path can have its operation mode changed over between a multiplex communication mode in which multiplex communication is made via an interface for use in multiplex transmission that is provided in the node and a sleep mode in which the interface is kept inoperative, and to a multiplex transmission apparatus for realizing the same. More particularly, the invention concerns an operation mode changing-over method which enables the operation mode to be changed over from the sleep mode to the multiplex communication mode without providing a transmission line for exclusive use on a seizing signal, and a multiplex transmission apparatus for realizing the same.
2. Related Art
In recent years, a multiplex transmission apparatus for performing multiplex communication is loaded on a vehicle, and this multiplex transmission apparatus is constructed with a plurality of nodes being connected to a common multiplex transmission path. Each node has provided therein an interface for use in multiplex communication for multiplexing data and making transmission and reception thereof, whereby transmission and reception of data are made between micro-controllers provided in their relevant nodes via the multiplex communication interface and the multiplex transmission path.
In order to maximally suppress the power consumption, each node has a changing-over function for making a changeover between a multiplex communication mode in which multiplex communication is performed via the multiplex transmission interface and a sleep mode in which the multiplex transmission interface is kept inoperative to decrease the current consumption.
At an ordinary time, the node is operated in the sleep mode to thereby suppress useless power consumption. When prescribed activation conditions have been satisfied, the operation mode is changed over, using a seizing signal, to the multiplex communication mode in which to permit the multiplex transmission interface to operate the micro-controller into its operational state.
FIG. 1 is a construction block diagram illustrating a conventional example of this type of multiplex transmission apparatus. In a multiplex transmission apparatus illustrated in FIG. 1, a plurality of nodes 102a to 102n are connected to a multiplex transmission path 103. A transmission line 104 for exclusive use on a seizing signal is provided separately from the multiplex transmission path 103 that is a data transmission line. Whereby, the node 102a transmits a seizing signal to all other nodes 102b to 102n via the transmission line 104 for exclusive use on a seizing signal.
When having received a seizing signal, each of the nodes 102b to 102n has its operation mode changed over from a sleep mode to a multiplex communication mode. As a result of this, every one of the nodes 102a to 102n has its operation mode transferred from the sleep mode to the multiplex communication mode, whereby bi-directional communication can be made between each node through the multiplex transmission path 103.
However, in the conventional multiplex transmission apparatus illustrated in FIG. 1, a transmission line for exclusive use on a seizing signal had to be provided separately from the multiplex transmission path. For this reason, there was the problem that the wire reduction effect resulting from the utilization of multiplex communication would be impaired.
On this account, as a technique that has solved this problem, a multiplex transmission apparatus that is described in Japanese Patent Application Laid-Open Publication No. H5-183562 is known. As illustrated in FIG. 2, in the multiplex transmission apparatus that is described in this Laid-Open Publication, nodes 114a, 114b, and 114c are connected to annular first and second transmission paths 112 and 113, whereby a controller 117 within each node 114a, 114b, and 114c transmits and receives a signal to and from another corresponding one via a multiplex module 115.
An activation circuit 120 for causing a seizing signal, which changes over the operational condition of the controller 117 from the sleep mode to the multiplex communication mode, to be input and output with respect to each corresponding one of the nodes 114a, 114b, and 114c is connected to the first transmission path 112. The activation circuit 120 has an input transistor 121 for inputting the seizing signal and an output transistor 122 for outputting the seizing signal.
In this construction, the controller 117 in the node 114a activates the multiplex module 115 and thereby activates the node 114a. On the other hand, the controller 117 outputs a seizing signal from its output terminal 126 to thereby make the output transistor 122 of the activation circuit 120 xe2x80x9conxe2x80x9d and thereby activate the nodes 114b and 114c. Namely, the nodes 114b and 114c can be activated by the input transistors 121 thereof being made xe2x80x9conxe2x80x9d. The controller 117 of the node 114a, when a prescribed waiting time length T0 has lapsed, outputs a transmission request frame via the multiplex module 115 and thereafter is transferred to the multiplex communication mode.
However, the multiplex transmission apparatus that is described in Japanese Patent Application Laid-Open Publication No. H5-183562 had the following problems.
(1) First, when at the time of the multiplex communication mode the input transistor 121 that is a reception portion of the starting circuit 120 is made xe2x80x9conxe2x80x9d, the current consumption inconveniently increases and the impedance of the transmission path varies. Namely, as a result of the xe2x80x9conxe2x80x9d operation of the input transistor 121, the impedance of the reception end decreases and this impedance ceases to match with the impedance of the transmission path. This is followed by the new problems that the signal is inconveniently reflected, the waveforms are distorted, the transmission data changes itself into a meaningless form, and the radiation noises increase.
(2) Further, at the time of activation, awaiting length of time is provided in order to prevent the element from being destroyed due to the phenomenon that the output transistor 122 that is a transmission portion and the output of the multiplex module 115 are short-circuited. This deteriorated the responsiveness to starting.
(3) Furthermore, since the output transistor 122 that is a transmission portion was provided in the activation circuit 120, the cost was increased by that extent.
It is an object of the present invention to provide an operational mode changing-over method that makes it possible to enhance the responsivity to activation without causing a increase in the current consumption and causing the occurrence of waveform distortions and that can be realized with an inexpensive construction, and a multiplex transmission apparatus for realizing the same.
To attain the above object, according to an aspect of the present invention, there is provided a multiplex transmission apparatus wherein a plurality of nodes are connected to a multiplex transmission path; each node performs communication, via an interface portion for use in multiplex transmission that has been provided therein, with another node; and each node has its mode that is changeable over between a multiplex communication mode for performing multiplex transmission and a sleep mode in which the interface portion is kept inoperative, each node comprising: a reception circuit that is connected to the multiplex transmission path and receives from the other node via the transmission path a seizing signal for making a changeover of the operation mode from the sleep mode to the multiplex communication mode; a mode changing-over portion that changes over the operation mode from the sleep mode to the multiplex communication mode according to the seizing signal received by the reception circuit to thereby cause the interface portion to operate in the multiplex communication mode, and a reception control portion for causing the reception circuit to make its xe2x80x9coffxe2x80x9d operation immediately after transfer to the multiplex communication mode.
According to this invention, when the reception circuit receives a seizing signal for making a changeover of the operation mode from the sleep mode to the multiplex communication mode from another node via the multiplex transmission path, the mode changing-over portion changes over the operation mode from the sleep mode to the multiplex communication mode according to the seizing signal received by the receiving circuit to thereby cause the interface portion to operate in the multiplex communication mode, while the reception control portion causes the reception circuit to make its xe2x80x9coffxe2x80x9d operation immediately after transfer to the multiplex communication mode.
Accordingly, at the time of the multiplex communication mode, the current consumption ceases to increase and, since the reception circuit is made xe2x80x9coffxe2x80x9d, the reception circuit ceases to have any effect on the multiplex transmission path. As a result of this, the waveform distortion ceases to occur in the multiplex transmission path.
In a preferred embodiment of the present invention, the interface portion is connected to the multiplex transmission path and, in a case where activating the other node, transmits the seizing signal to the other node via the multiplex transmission path.
According to this embodiment, since the interface portion in the case of activating the other node, transmits the seizing signal to the other node via the multiplex transmission path, the responsivity to activation of the node can be improved and, in addition, it becomes unnecessary to provide a special transmission circuit, with the result that the cost becomes low.
In a preferred embodiment of the present invention, the reception circuit comprises a first transistor circuit that is connected to the multiplex transmission path and that makes its xe2x80x9conxe2x80x9d operation upon input of the seizing signal and outputs an output voltage to the mode changing-over portion, and a second transistor circuit that is connected in series to the first transistor circuit and that makes its xe2x80x9conxe2x80x9d operation when the operation mode is in the sleep mode and, immediately after transfer to the multiplex communication mode, makes its xe2x80x9coffxe2x80x9d operation upon receipt of a reception control signal from the reception control portion, and, through the xe2x80x9coffxe2x80x9d operation, causes the first transistor circuit to make its xe2x80x9coffxe2x80x9d operation.
According to this embodiment, when the first transistor circuit makes its xe2x80x9conxe2x80x9d operation upon input of the seizing signal and outputs an output voltage to the mode changing-over portion, the mode changing-over portion makes a change-over of the operation mode from the sleep mode to the multiplex communication mode. As a result of this, the second transistor circuit, immediately after transfer to the multiplex communication mode, makes its xe2x80x9coffxe2x80x9d operation upon receipt of a reception control signal from the reception control portion, and, through this xe2x80x9coffxe2x80x9d operation, causes the first transistor circuit to make its xe2x80x9coffxe2x80x9d operation. Therefore, at the time of the multiplex communication mode, the current consumption ceases to increase and, since the reception circuit is made xe2x80x9coffxe2x80x9d, the reception circuit ceases to have any effect on the multiplex transmission path. As a result of this, the waveform distortion ceases to occur in the multiplex transmission path.
In a preferred embodiment of the present invention, the plurality of the nodes are connected to the multiplex transmission path in the form of a ring.
According to this embodiment, since the plurality of nodes are connected to a ring-like multiplex transmission path, even when part of the multiplex transmission path is broken, all the nodes can be activated if transmitting the seizing signal in the opposite direction.
To attain the above object, according to another aspect of the present, there is provided an operation mode changing-over method wherein in each of a plurality of nodes connected to a multiplex transmission path, changeover is made between a multiplex communication mode for performing multiplex transmission and a sleep mode in which an interface portion is kept inoperative, the operation mode changing-over method comprising the steps of: receiving by a reception circuit via the multiplex transmission path a seizing signal for making a changeover of the operation mode from the sleep mode to the multiplex communication mode; changing over the operation mode from the sleep mode to the multiplex communication mode according to the seizing signal received by the reception circuit to thereby cause the interface portion to operate in the multiplex communication mode, and causing the reception circuit to make its xe2x80x9coffxe2x80x9d operation immediately after transfer to the multiplex communication mode.